Dual plunger gooseneck for magnesium die casting

ABSTRACT

A mechanical apparatus and method for the casting of metal components is disclosed. The apparatus includes a gooseneck having dual plungers for drawing molten metal from a crucible of hot metal and for forcing the drawn molten metal through the system, a hot runner assembly having a thermal valve developed in time and positioned adjacent the mold cavity, and a machine nozzle positioned between the gooseneck and the hot runner assembly. The dual plunger is fitted with a shot plunger and a shutoff plunger which work in conjunction to allow for molten metal to be drawn into the gooseneck but to stop its passage into the gooseneck when the metal is forced through the system into the die. Both temperature and flow rate are carefully monitored and controlled. Two embodiments of the gooseneck are provided in which the positions of the shot plunger and the shutoff plunger are altered and in which the molten metal is drawn into the gooseneck at different locations.

GOVERNMENT CONTRACT INFORMATION

This invention was made with United States Government support awarded by the following program, agency and contract: NIST Advanced Technology Program, the United States Department of Commerce, Contract No. 70NANBOH3053. The United States has certain rights in this invention.

TECHNICAL FIELD

The present invention relates generally to the casting of magnesium components. More particularly, the present invention relates to a method and apparatus for die-casting magnesium components from molten magnesium using a hot runner system in which both temperature and flow rate are controlled.

BACKGROUND OF THE INVENTION

Magnesium is an attractive material for application in motor vehicles because it is both a strong and lightweight material. The use of magnesium in motor vehicles is not new. Race driver Tommy Milton won the Indianapolis 500 in 1921 driving a car with magnesium pistons. A few years after that magnesium pistons entered mainstream automotive production. By the late 1930's over 4 million magnesium pistons had been produced. Even in the early days of car production, the weight-to-strength ratio of magnesium, compared with other commonly-used materials, was well-known.

Considering the recent increase in fuel prices driven largely by increased global demand, more attention is being given to any practical and economically viable step that can be taken to reduce vehicle weight without compromising strength and safety. Accordingly, magnesium is increasingly becoming an attractive alternative to steel, aluminum and polymers, given its ability to simultaneously meet crash-energy absorbing requirements while reducing the weight of vehicle components. Having a density of 1.8 kg/L, magnesium is 36% lighter per unit volume than aluminum (density=2.70 kg/L) and is 78% lighter per unit volume than steel (density=7.70 kg/L). Magnesium alloys also hold a competitive weight advantage over polymerized materials, being 20% lighter than most conventional glass reinforced polymer composites.

Beyond pistons, numerous other vehicle components are good candidates for being formed from magnesium, such as inner door panels, dashboard supports and instrument panel support beams. In the near-term it is anticipated that components made from magnesium for high volume use in the motor vehicle might also include powertrain, suspension and chassis components.

The fact that the surface “skin” of die-cast magnesium has better mechanical properties over the bulk than more commonly used materials, thinner (ribbed) and lighter die-castings of magnesium enables products to meet their functional requirements. Such components can have sufficiently high strength per unit area to compete with more common and heavier aluminum and plastic components. Furthermore, magnesium has considerable manufacturing advantages over other die-cast metals, such as aluminum, being able to be cast closer to near net-shape thereby reducing the amount of material and associated costs. Particularly, components can be routinely cast at 1.0 mm to 1.5 mm wall thickness and 1 to 2 degree draft angles, which are typically ½ that of aluminum. The extensive fluid flow characteristics of magnesium offers a single, large casting to replace a plurality of steel fabrications. Magnesium also has a lower latent heat and reduced tendency for die pick-up and erosion. This allows a reduced die-casting machine cycle time (˜25% higher productivity) and 2 to 4 times longer die life (from 150-200,000 to 300-700,000 shots) compared with that of aluminum casting.

However, the use of magnesium in automotive components is burdened with certain drawbacks. While magnesium is abundant as a natural element, it is not available at a level to support automotive volumes. This situation causes hesitation among engineers to design and incorporate magnesium components. On the occasion when the magnesium is selected as the material of choice, designers fail to integrate die-casting design with manufacturing feasibility in which the mechanical properties, filling parameters, and solidification profiles are integrated to predict casting porosity and property distribution.

The raw material cost of magnesium relative to other commonly used materials is also an impediment to mass implementation in the automotive industry. Current techniques for casting parts from magnesium make expanding the use of magnesium into a broader array of products less attractive. Presently, all large die-castings are produced in high pressure, cold-chamber machines where the metal is injected from one central location. This approach results in inferior material properties and waste material.

Accordingly, in order to make the use of magnesium in the production of vehicle components more attractive to manufacturers, a new approach to product casting is needed. This new approach is the focus of the present invention.

SUMMARY OF THE INVENTION

The present invention represents advancement in the die casting process of magnesium and similar metals. The primary objective of the present invention is to provide a multi-point injection hot runner system for introducing molten magnesium into production die cavities at a controlled temperature and flow rate. The method and apparatus of the present invention provides an approach that minimizes wastage while maximizing manufacturing repeatability thus providing a cost-effective and practical answer to the problems ordinarily associated with known approaches to the formation of articles from magnesium.

The present invention accomplishes these and other objectives by providing a self-contained, self-enclosed system which maximizes control over heat and molten metal flow while minimizing contamination. The system utilizes a gooseneck having dual plungers that draws molten metal from a crucible and directs the molten metal to a hot runner assembly via a machine nozzle. The dual plunger comprises a shot plunger and a shutoff plunger. The shot plunger draws the molten metal from the crucible and drives it through the system. The shutoff plunger works in concert with the shot plunger to regulate flow of molten metal both into and out of the gooseneck. The molten metal exits the hot runner assembly through a hot runner tip into a mold cavity. The hot runner assembly is provided to gate directly on or very near the part surface.

Each of the machine nozzle, the hot runner assembly, and the hot runner tip is heated by adjacent heating elements which may be coil heaters, tubular heaters or band heaters or a variety of such heating elements. By providing such an array of heaters the temperature of the molten metal can be readily and accurately maintained.

Flow of the molten metal is regulated by use of the gooseneck which incorporates the shutoff plunger and the shot plunger. The shutoff plunger and the shot plunger are selectively positioned so as to draw molten metal from a crucible into which the plunger is at least partially submerged. Once the gooseneck is filled with molten metal the molten metal is forced under pressure by movement of the shot plunger out of the gooseneck and into the machine nozzle. A preferred and accurate pressure is maintained by the amount of force applied by the piston upon the molten metal. This pressure is maintained evenly throughout the system such that the molten metal moves at a constant, regulated flow out of the gooseneck and through the machine nozzle, the hot runner assembly, the hot runner tip, and into the cavity.

To maintain this constant pressure or zero pressure difference by avoiding the return of molten metal back into the gooseneck when the piston extracts or moves to apply pressure to the molten metal, the shutoff plunger is moved to prevent such an outflow. During the extraction step a thermal valve (“TV”) is formed at the tip of the hot runner assembly, thus preventing flow of molten metal from the mold cavity and back into the hot runner tip. The formation of the blockage at the tip of the thermal valve is accomplished by a balance of both temperature regulation and tip opening geometry. With this arrangement the molten metal is retained in and completely fills entire feeding system. This is necessary because magnesium molten metal needs to be present in the machine nozzle at all times, before and after each shot.

Flow of the molten metal is regulated by use of the dual plunger which incorporates an internal reciprocating plunger to selectively draw molten metal from a crucible into which the dual plunger gooseneck is at least partially submerged. As briefly noted above, the shutoff plunger works in concert with the shot plunger to allow the selective entry and exit of fluid into and out from the gooseneck. By being moved to a fluid flow passing position to fill the gooseneck, the shutoff plunger is open to allow the passage of fluid from the crucible while the shot plunger draws metal into the gooseneck. Once the filling of the gooseneck is complete, the shutoff plunger is moved to a fluid-closed position. In this position the molten metal is allowed to pass thereby under pressure of the shot plunger. A preferred and accurate pressure is maintained by the amount of force applied by the shot plunger upon the molten metal. This pressure is maintained accordingly throughout the system such that the molten metal moves at a constant, regulated flow out of the gooseneck and through the machine nozzle, the hot runner assembly, out of the hot runner tip and into the cavity. With this arrangement the molten metal is retained in the entire feeding system. This is necessary because molten magnesium metal is expected to be filled 100% in the machine nozzle at all times, before and after each shot.

The present invention teaches an arrangement of the dual plunger system which includes a shot plunger reciprocatingly provided in a shot plunger cylinder and a shutoff plunger reciprocatingly provided in a shutoff plunger cylinder. The shot plunger cylinder and the shutoff plunger cylinder as part of the gooseneck are substantially parallel to one another. The shot plunger is movable between a molten metal drawing position and a molten metal injecting position. The shutoff plunger is movable between a molten metal halting position and a molten metal passing position. In operation, the shutoff plunger is moved to its molten metal passing position while the shot plunger moves to its molten metal drawing position whereby molten metal is drawn into the shot plunger cylinder and the gooseneck. Thereafter the shutoff plunger is moved to its molten metal halting position and the shot plunger is moved to its molten metal shot injecting position whereby molten metal is forced by the shot plunger for injection into the mold cavity.

By providing a mechanical apparatus and a method according to the present invention several advantages are achieved. First, the quality and consistency of die castings is improved. Second, reductions in cycle time are achieved. Third, less waste and less recycling of material is achieved. Fourth, the present invention reduces the level of maintenance required as compared with known systems.

Other advantages and features of the invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference should now be made to the embodiment illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention wherein:

FIG. 1 illustrates a diagrammatic view of a casting apparatus utilizing the gooseneck with dual plungers according to the present invention;

FIG. 2 illustrates a sectional view of a hot runner assembly in position relative to a die according to the present invention;

FIG. 3 illustrates a sectional view of the hot runner body of FIG. 2 illustrating an alternate arrangement for heating;

FIG. 4 illustrates a sectional view of the hot runner tip according to the present invention in relation to a portion of a cast part;

FIG. 5 illustrates a perspective and partially sectioned view of a machine nozzle according to the present invention;

FIG. 6 illustrates a sectional view of a first preferred embodiment of a gooseneck according to the present invention, illustrating the gooseneck filling mode;

FIG. 7 illustrates the same view of FIG. 6 but shows the gooseneck in its shot mode;

FIG. 8 illustrates a side view of the shutoff plunger of the preferred embodiment of the present invention;

FIG. 9 illustrates an end view of the shutoff plunger shown in FIG. 8;

FIG. 10 illustrates a sectional view of a modified version of the first preferred embodiment of the present invention;

FIG. 11 illustrates a sectional view of a second preferred embodiment of a gooseneck according to the present invention in its filling mode;

FIG. 12 illustrates the same view of FIG. 11 but shows the gooseneck in its metal injection mode; and

FIG. 13 illustrates a sectional view of a modified version of the second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following figures, the same reference numerals will be used to refer to the same components. In the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting.

With reference to FIG. 1, a diagrammatic view of the hot chamber apparatus of the present invention is illustrated, being generally illustrated as 10. The apparatus 10 is entirely self-enclosed, preventing atmospheric exposure of the liquid melt. It is to be understood that while the present invention is directed at the formation of components from molten magnesium alloy, other metals including zinc may be used.

The hot chamber 10 includes a casting die 12. The casting die 12 includes a cover half 14 and an ejector half 16, a hot runner assembly 18 partially recessed within the cover half 14 of the casting die 12, a gooseneck 19, a shot plunger 20 operatively associated with the gooseneck 19, a shutoff plunger 21 also operatively associated with the gooseneck 19, and a machine nozzle 22 fitted between the hot runner assembly 18 and the gooseneck 19. A substantial portion of the gooseneck 19 is submerged within a crucible 24 of molten metal.

Referring now to FIG. 2, a sectional and detailed view of the hot runner assembly 18 is illustrated. As noted above, the hot runner assembly 18 is partially recessed within the cover half 14 of the casting die 12. The hot runner assembly 18 consists of a hot runner body 26 having a long axis along which a molten metal passage 28 is formed. The hot runner body 26 includes a molten metal input end 30 and a molten metal output end 32. The molten metal input end 30 includes an outer cone 34 which can be inserted into a receiving end of the machine nozzle 22 as shown in FIG. 5 and as discussed in relation thereto.

With reference still to FIG. 2, the molten metal output end 32 includes a cavity 36 defined therein into which a hot runner tip 38 is partially positioned. The outward end of the hot runner tip 38 terminates at a part line 39 formed between the cover half 14 and ejector half 16 of the casting die 12. The hot runner tip 38 includes an end 41 that is open to the mold cavity.

The hot runner tip 38 is provided to establish thermal valving in the apparatus 10 whereby a thermal plug (shown in FIG. 4 and discussed in relation thereto) is formed at the orifice outlet of the hot runner body 26. The opening of the hot runner tip 38 may be of a variety of possible sizes, although an orifice size of about 8 mm provides an effective configuration. The objective of the hot runner tip 38 is to prevent the flow of molten magnesium downwards into the gooseneck 19 during each complete casting cycle because of the ability of the thermal plug formed adjacent the die cavity by the hot runner tip 38 to retain the pressure difference in the hot runner assembly 18 and the gooseneck 19.

The hot runner body 26 is positioned in a hot runner body cavity 40 which is recessed within the cover half 14 of the casting die 12. The hot runner body cavity 40 is held in place by a support ring 42 which may be fastened to the cover half 14 of the casting die 12 by conventional means such as by mechanical fasteners 44 and 44′.

It is important in the operation of the apparatus 10 that the molten metal be maintained at high temperatures at all stages between the crucible 24 and the die 12. Accordingly, a series of insulators and heaters are provided to maintain the needed temperatures. To this end the hot runner assembly 18 includes both insulators and heaters. A hot runner body insulator ring 46 is fitted between the hot runner body 26 and the support ring 42. A thermal valve insulator ring 49 is fitted between the hot runner tip 38 and the cover half 14 of the casting die 12. The hot runner body insulator ring 46 and the thermal valve insulator ring 49 are formed from known insulating material.

To keep the hot runner assembly 18 as uniform a temperature as possible external heaters are applied. As illustrated in FIG. 2, a pair of spaced-apart band heaters 48 and 50 is fitted to the hot runner body 26. The band heaters 48 and 50 are electrically powered and controlled in a known manner.

In addition or as an alternative to the use of band heaters as illustrated in FIG. 2, coil or tubular heaters may also be used to create and maintain the desired level of heat in the hot runner assembly 18. An example of such an alternative is illustrated in FIG. 3 where a coil heater 52 is fitted to the hot runner body 26 in lieu of the band heater 48. As a further modification, a hot runner tip band heater 54 is shown in FIG. 3 externally positioned on the hot runner tip 38. Other variations may be possible provided the objective of establishing and regulating the desired levels of heat with respect to the hot runner body 26 is achieved. Accordingly, the application of heat using bands and coils as shown is intended as being illustrative and not limiting.

Referring now to the hot runner tip 38, this component is illustrated in sectional view in FIG. 4 and is shown in relation to a portion of a cast part “P”. The cast part P is illustrated as having been removed from the mold cavity and thus separated from the hot runner tip 38. A molten metal passage 58 is defined along the long axis of the hot runner tip 38. The hot runner tip 38 may be threadably attached to the hot runner body 26 or may be attached by other mechanical means.

The hot runner tip heater 54 is provided to keep the hot runner tip 38 at a pre-selected temperature such that the metal at the end 41 may flow freely into the mold cavity during the plunger shot but will form a solid blockage once the shot is completed. Accordingly, there is a temperature differential between the end 41 and the hot runner tip 38. This temperature differential means that the area of the opening of the hot runner tip 38 into the mold cavity will be cooler than the rest of the hot runner tip 38, thus allowing the molten metal in the immediate area of the tip to cool and become solidified locally in the area of the tip. This arrangement prevents molten metal from leaking from the cavity and back into the hot runner tip 38 at the end of the shot.

The temperature differential is dependent upon the metal being used to make the cast component. By way of example, magnesium alloy (for example, AZ91) becomes solid at 470° C. and is fully molten at temperatures over 595° C. Accordingly, the temperature of the hot runner tip 38 must be such that the metal therein is molten to allow it to flow. Conversely, the temperature at the end 41 of the hot runner tip 38 that is open to the mold cavity must be cooler than that of the rest of the hot runner tip 38 and specifically must approach, but not necessarily meet, the temperature of 470° C. at which magnesium alloy is solid. Of course, the temperature of the thermal valve 38 may be adjusted up or down depending on the metal alloy being used.

As illustrated in FIG. 4, a thermal valve “TV” of an ideal size and configuration has been formed within the hot runner tip 38. The thermal valve TV prevents the back-flow of molten metal into the hot runner tip 38 after the completion of the shot.

The machine nozzle 22 is illustrated in FIG. 5. A quarter of the machine nozzle 22 has been removed for illustrative purposes. The machine nozzle 22 includes a machine nozzle body 60 having a molten metal passage 62 defined along its long axis. The machine nozzle 22 also includes a molten metal input end 64 which has an outer cone 68 to mate with the gooseneck 19. The machine nozzle 22 also has a molten metal output end 66 defined as a conical cavity 70 which mates with outer cone 34 of the molten metal input end 30 of the hot runner assembly 18.

As noted above, it is important to establish and maintain desired temperatures at all points between the crucible 24 and the die 12. Accordingly, the machine nozzle 22 is also provided with a heating element. Two forms of heating elements are illustrated in FIG. 5. The first form is heating element 72 which is a coil-type heating system. The second form is heating element 73 which is a band heater. The coil, band, or tubular form of heating elements may be used, alone or in combination.

Delivery of the molten metal from the crucible 24 to the machine nozzle 22 is accomplished by the gooseneck which is presented herein in two embodiments. The first embodiment of the gooseneck of the present invention, generally illustrated as 19, is illustrated in FIGS. 6 and 7 with a variation of this embodiment illustrated in FIG. 10. A second embodiment of the gooseneck of the present invention, generally illustrated as 110, is illustrated in FIGS. 11 and 12 with a variation of this embodiment shown in FIG. 13. In either embodiment, the body of the gooseneck may be made of a superalloy steel.

Referring to FIGS. 6 and 7, the gooseneck 19 includes a plunger body 74. The plunger body 74 includes a shot plunger cylinder 76 and a molten metal passageway 78 through which the molten metal flows out of the plunger body 74. The shot plunger cylinder 76 and the molten metal passageway 78 are substantially parallel to one another, with the diameter of the shot plunger cylinder 76 being larger than the diameter of the molten metal passageway 78.

The molten metal passageway 78 includes an inlet end 80 and an outlet end 82. The inlet end 80 is in fluid communication with the shot plunger cylinder 76 by way of a molten metal channel 84. The outlet end 82 terminates at a plunger molten metal outlet port 86. The plunger molten metal outlet port 86 is preferably of a conical configuration as illustrated so as to mate snugly with the outer cone 68 of the molten metal input end 64 of the machine nozzle 22.

The shot plunger 20 having a pair of spaced apart sacrificial rings 89, 89′ is reciprocatingly provided within the shot plunger cylinder 76. The shot plunger 20 is selectively driven by a plunger drive shaft 90. The plunger drive shaft 90 is operatively associated with a plunger drive mechanism (not shown). The sacrificial rings 89, 89′ are provided to take up wear endured as the shot plunger 20 reciprocates within the shot plunger cylinder 78 during normal operations, thus saving the shot plunger 20 from wear. After a given number of cycles the gooseneck 19 is disassembled and the worn sacrificial rings 89, 89′ are replaced by a new set.

The shot plunger cylinder 76 includes a molten metal passageway 92 which is fluidly connected with a shutoff plunger cylinder 94. The shutoff plunger cylinder 94 is generally parallel with both the shot plunger cylinder 76 and the molten metal passageway 78. The shutoff plunger cylinder 94 includes a molten metal inlet 96 which is in fluid communication with the crucible 24 of molten metal (shown in FIG. 1).

A shutoff plunger 21 is reciprocatingly provided within the shutoff plunger cylinder 94. The shutoff plunger 21 is selectively driven by a shutoff plunger drive shaft 100. The shutoff plunger 21 has an upper set of sacrificial shutoff rings 102, 102′, and 102″ and a lower set of sacrificial shutoff rings 104, 104′, and 104″. Like the sacrificial rings 89 and 89′ fitted to the shot plunger 20, the sacrificial rings 102, 102′, 102″, 104, 104′, and 104″ are provided to suffer wear instead of the shutoff plunger 21. They may also be replaced along with the sacrificial rings 89 and 89′ after a predetermined number of cycles. The shutoff plunger 21 is operatively associated with a shutoff plunger drive mechanism (not shown).

In FIG. 6 the gooseneck 19 is illustrated in its filling position in which the shutoff plunger 21 having been moved upward as indicated by the arrow to its fluid passing position such that the upper set of sacrificial shutoff rings 102, 102′, and 102″ is above the molten metal inlet 96 and the lower set of sacrificial shutoff rings 104, 104′, and 104″ is below the molten metal passageway 92. Once in this position, the shot plunger 20 is drawn upward as illustrated by the arrow. This movement creates suction within the shot plunger cylinder 76, the suction effecting the movement of molten metal (not shown) from the crucible 24, through the molten metal inlet 96, through the molten metal passageway 92, and into the shot plunger cylinder 76. The shot plunger 20 continues its upward movement until the requisite amount of molten metal has been drawn into the shot plunger cylinder 76. Because of the formation of the thermal valve TV the flow of molten metal back into the system is prevented as there is no pressure differential within the system between the hot runner assembly and the shot plunger cylinder 76.

In FIG. 7 the shutoff plunger 21 has been moved as illustrated by the arrow to its fluid flow blocking position such that the upper set of sacrificial shutoff rings 102, 102′, and 102″ is below the molten metal inlet 96. Once in this position the shot plunger 20 is moved downward as illustrated by the arrow. This movement creates pressure within the shot plunger cylinder 76, forcing the molten metal out of the shot plunger cylinder 76, through the molten metal passageway 78, and out of the outlet end 82 of the gooseneck 19 and into the machine nozzle 22 (not shown).

The shutoff plunger 21 is illustrated in FIG. 8. With reference thereto, the threaded attachment of the shutoff plunger drive shaft 100 is shown. It is to be understood that while each of the upper set of sacrificial shutoff rings 102, 102′, and 102″ and the lower set of sacrificial shutoff rings 104, 104′, and 104″ is composed of three spaced apart rings, a greater or lesser number of rings may be employed.

An end view of the shutoff plunger 21 the sacrificial shutoff ring 104″ is illustrated in FIG. 9. A series of molten metal passageways 106 are formed in the lower set of rings 104 (as well as the upper set of rings 102). The molten metal passageways 106 are provided to allow some molten metal to flow within the shutoff plunger cylinder 94 thereby providing partial equalization of pressure throughout the gooseneck 19 to prevent extreme system pressure differentials which might result in slowed reciprocation of the shutoff plunger 21.

As noted above with reference to FIG. 6, a pair of sacrificial rings 89 and 89′ is provided to endure the operational wear instead of the shot plunger 20. This wear is the result of the metal-to-metal contact between the sacrificial rings 89 and 89′ and the wall of the shot plunger cylinder 76. Similarly, the sacrificial shutoff plunger rings 102, 102′, 102″, 104, 104′, and 104″ are provided to prevent wear on the shutoff plunger 21. An alternative approach to the use of the sacrificial rings on either the shot plunger 20 or on the shutoff plunger 21 is illustrated in FIG. 10 where a gooseneck 19′ is illustrated. The gooseneck 19′ includes a plunger body 74′, a shot plunger cylinder 76′, a shot plunger 20′, a shutoff plunger cylinder 94′, and a shutoff plunger 21′. With the exception of the design and construction of the plunger body 74′, the shot plunger cylinder 76′, the shot plunger 20′, the shutoff plunger cylinder 94′, and the shutoff plunger 21′, the gooseneck 19′ includes elements that are preferably identical in design and function to those of the gooseneck 19 discussed above and shown in FIGS. 6 and 7. Accordingly, only the differences will be discussed.

The plunger body 74′ is configured so as to eliminate the need of having to change sacrificial rings. Accordingly, the shot plunger 20′ and the shutoff plunger 21′ are provided without sacrificial rings. This is accomplished by use of a shot plunger ceramic liner 105 provided to line the shot plunger cylinder 76′. Similarly, a shutoff plunger ceramic liner 107 is provided to line the shutoff plunger cylinder 94′. The ceramic liners 105 and 107 are sleeves that are shrink-fitted within the plunger body 74′. The ceramic liners 105 and 107 may be composed of a variety of ceramic materials, but preferably are composed of a silicon nitride material such as SN-240 manufactured by Kyocera. Other ceramic materials may be used in the alternative. By using ceramic liners in the gooseneck 19′ the metal-to-metal wear of the arrangement of the gooseneck 19 is eliminated.

An alternate embodiment of the dual plunger design of the present invention presented above is illustrated in FIGS. 11 and 12. According to this embodiment, the gooseneck 110 includes a plunger body 114. The plunger body 114 includes a molten metal passageway 116 through which molten metal flows out of the plunger body 114. Adjacent the molten metal passageway 116 is a shutoff plunger cylinder 118 housing therein a reciprocating shutoff plunger 120. The shutoff plunger 120 includes an upper set of sacrificial rings 122, 122′, and 122″ and a lower set of sacrificial rings 124, 124′, and 124″. The shutoff plunger 120 is selectively driven by a shutoff plunger drive shaft 126. The shutoff plunger 120 is operatively associated with a shutoff plunger drive mechanism (not shown).

Adjacent the shutoff plunger cylinder 118 is a plunger cylinder 128. A shot plunger 129 selectively driven by a plunger drive shaft 132 is reciprocatingly provided within the plunger cylinder 128. The plunger drive shaft 132 is operatively associated with a plunger drive mechanism (not shown). The plunger 129 includes a set of sacrificial rings 130, 130′, and 130″.

A molten metal fluid passageway 134 is formed between the molten metal passageway 116 and the shutoff plunger cylinder 118. Another molten metal fluid passageway 136 is formed between the shutoff plunger cylinder 118 and the plunger cylinder 128. A molten metal inlet 138 is formed at the lower end of the shutoff plunger cylinder 118 and is open to the crucible 24 of molten metal (shown in FIG. 1).

In FIG. 11, as illustrated by the arrow, the shutoff plunger 120 has been moved to its fluid flow passing position such that the lower set of rings 124, 124′, and 124″ are positioned above the molten metal fluid passageway 136. Once the shutoff plunger 120 is so positioned, the plunger 129 is moved upward as indicated by the arrow thereby creating suction within the plunger cylinder 128. Molten metal travels from the crucible 24 into the plunger cylinder 128 via the molten metal inlet 138 defined at the base of the gooseneck 110. The plunger 129 continues its upward travel in the direction of the arrow until the plunger cylinder 128 is filled with molten metal.

In FIG. 12 the shutoff plunger 120 has been moved in the direction of the arrow to its fluid halting position such that the lower set of rings 124, 124′, and 124″ is below the molten metal fluid passageway 136 and the upper set of rings 122, 122′, and 122″ is above the molten metal fluid passageway 134. Once the shutoff plunger 120 is in its fluid halting position, the shot plunger 129 is moved downward as indicated by the arrow. This movement of the shot plunger 129 forces the molten metal through the molten metal passageway 136, around and by the shutoff plunger 120, into and through the molten metal passageway 116 and out of the gooseneck 110 to the machine nozzle 22 (shown in FIG. 1).

As an alternative to the embodiment shown in FIGS. 11 and 12, the sacrificial rings on the shot plunger 129 and the shutoff plunger 120 may be eliminated in favor of ceramic linings as discussed above in relation to FIG. 10. This alternative is shown in FIG. 13. A gooseneck 110′ is shown and includes a plunger body 114′, a shot plunger cylinder 128′, a shot plunger 129′, a shutoff plunger cylinder 118′, and a shutoff plunger 120′. With the exception of the design and construction of the plunger body 114′, the shot plunger cylinder 128′, the shot plunger 129, the shutoff plunger cylinder 128′, and the shutoff plunger 120′, the gooseneck 110′ includes elements that are preferably identical in design and function to those of the gooseneck 110 discussed above and shown in FIGS. 11 and 12. The differences are discussed hereafter.

According to the embodiment shown in FIG. 13, the plunger body 114′ eliminates the need for the sacrificial rings shown in FIGS. 11 and 12. A shot plunger ceramic liner 140 is provided in the shot plunger cylinder 128′. A shutoff plunger ceramic liner 142 is provided to line the shutoff plunger cylinder 118′. Like the shutoff liners 105 and 107 of the gooseneck 19′ discussed above, the liners 140 and 142 are sleeves that are shrink-fitted within the gooseneck 110′

The arrangements shown of the goosenecks 19 and 110 illustrated in their respective figures and in their variations provided a positive method for assuring that a constant flow of molten metal at a constant pressure can be maintained in the hot chamber 10 at all times. This arrangement assures that no back flow of molten metal out of the system and back into the crucible 24 can occur.

The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims. 

1. A dual plunger gooseneck for use in metal casting, the gooseneck comprising: a plunger body; a shot plunger cylinder formed in said plunger body; a shot plunger reciprocatingly fitted in said shot plunger cylinder, said shot plunger being movable between a molten metal drawing position and a molten metal injecting position; a shutoff plunger cylinder formed in said plunger body; and a shutoff plunger reciprocatingly fitted in said shutoff plunger cylinder, said shutoff plunger being movable between a molten metal flow blocking position and a molten metal flow passing position.
 2. The dual plunger gooseneck of claim 1 wherein said shot plunger cylinder has a long axis and said shutoff plunger cylinder has a long axis, said axes being parallel.
 3. The dual plunger gooseneck of claim 1 wherein said shot plunger includes a sacrificial ring.
 4. The dual plunger gooseneck of claim 1 wherein said shutoff plunger includes a sacrificial ring.
 5. The dual plunger gooseneck of claim 1 wherein said shot cylinder is lined with a ceramic liner.
 6. The dual plunger gooseneck of claim 1 wherein said shutoff cylinder is lined with a ceramic liner.
 7. The dual plunger gooseneck of claim 1 wherein said shutoff cylinder includes a molten metal passageway.
 8. The dual plunger gooseneck of claim 1 further including a molten metal outlet passageway.
 9. The dual plunger gooseneck of claim 8 wherein said molten metal outlet passageway is in fluid communication with said shutoff plunger cylinder.
 10. An apparatus for the casting of metal in a mold cavity defined between a cover die and an ejector die, the apparatus comprising: a crucible containing a liquid metal; a dual plunger gooseneck including a shot plunger cylinder, a shot plunger, said shot plunger being reciprocatingly fitted within said shot plunger cylinder, a shutoff plunger cylinder, and a shutoff plunger, said shutoff plunger being reciprocatingly fitted within said shutoff plunger cylinder, said dual plunger gooseneck including a molten metal inlet and a molten metal outlet, said molten metal inlet being in fluid communication with said crucible; a hot runner being at least partially recessed within the cover die half, said hot runner having a molten metal passageway formed therethrough, said molten metal passageway of said hot runner having an inlet and an outlet, said inlet of said molten metal passageway being in fluid communication with said outlet of said shot plunger; and a hot runner tip operatively associated with said outlet of said hot runner.
 11. The dual plunger gooseneck of claim 10 wherein said shot plunger cylinder has a long axis and said shutoff plunger cylinder has a long axis, said axes being parallel.
 12. The apparatus of claim 10, further including a machine nozzle having a molten metal passageway formed therethrough, said molten metal passageway of said machine nozzle having an inlet and an outlet, said inlet of said machine nozzle being in fluid communication with said outlet of said plunger.
 13. The apparatus of claim 10 wherein said shot plunger is fitted with at least two spaced apart sacrificial rings.
 14. The apparatus of claim 10 wherein said shutoff plunger is fitted with at least two spaced apart sacrificial rings.
 15. The apparatus of claim 10 further including a shot plunger cylinder liner.
 16. The apparatus of claim 15 wherein said liner is formed from a ceramic material.
 17. The apparatus of claim 10 further including a shutoff plunger cylinder liner.
 18. The apparatus of claim 17 wherein said liner is formed from a ceramic material.
 19. The apparatus of claim 10 further including a heating element fitted to said machine nozzle.
 20. The apparatus of claim 19 wherein said heating element is selected from the group consisting of a band heater, a tube heater, and a tubular heater.
 21. The apparatus of claim 10 further including a heating element fitted to said hot runner.
 22. The apparatus of claim 21 wherein said heating element is selected from the group consisting of a band heater, a tube heater, and a tubular heater.
 23. The apparatus of claim 10 further including a heating element fitted to said hot runner tip.
 24. The apparatus of claim 23 wherein said heating element is selected from the group consisting of a band heater, a tube heater, and a tubular heater.
 25. A method for casting a metal part in a die cavity defined between a lower die and an upper die, the method comprising the steps of: forming a metal part casting apparatus comprising a crucible containing a liquid metal, a dual plunger gooseneck, said dual plunger gooseneck having a shot plunger and a shutoff plunger, a hot runner, and a hot runner tip having a heating element and a tip opening adjacent the die cavity, said shot plunger being movable between a liquid metal drawing position and a liquid metal injecting position, said shutoff plunger being movable between a liquid metal flow blocking position and a liquid metal flow passing position; applying energy to said heating elements to effect heating of said hot runner tip to a pre-selected temperature; moving said shutoff plunger to said liquid metal flow passing position and moving said shot plunger to said liquid metal drawing position whereby liquid metal is drawn from said crucible into said dual plunger gooseneck; moving said shutoff plunger to said liquid metal flow blocking position and moving said shot plunger to said liquid metal injecting position to force said liquid metal through said hot runner and said thermal valve and into the mold cavity; and regulating the temperature of said hot runner tip to form a substantially solid blockage within said hot runner tip after said step of forcing said liquid metal through said hot runner and said hot runner tip. 